De Morgan's laws

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De Morgan's laws

pl n
(Logic) (in formal logic and set theory) the principles that conjunction and disjunction, or union and intersection, are dual. Thus the negation of P & Q is equivalent to not-P or not-Q
[named after Augustus De Morgan (1806–71), British mathematician]
References in periodicals archive ?
We have at once that [[intersection].sub.j = 1 to k] [X.sub.j] = [phi] by DeMorgan's law on algebra of sets [5], completing the necessity part.
Again appealing to DeMorgan's law we have V = [union].sub.j = 1 to k] (V-[X.sub.j]), whence [E.sup.c] fills out V.